It is commonplace in processing industries to require that electronic and other control equipment be enclosed in explosion-proof housings. Typically, these housings are formed of aluminum or steel materials and are formed with a lengthy or labyrinthine path between the various parts making up the housing so as to provide a long escape path for hot gases generated within the housing due to an explosion, so that the gases are cooled by the time they reach the outside of the container, thus preventing ignition of any combustible materials outside the housing.
Frequently these housings are intended to be used in corrosive atmospheres, such that their materials are subject to chemical attack. Of course, it would be possible to make the housings out of metals which resist chemical attack, but these refractory metals are very difficult to fabricate; while plastic materials are insufficiently strong. Accordingly, the art requires a corrosion-proof, explosion-proof housing. This requires that the entire exterior surface of the housing be provided with a coating of a corrosion-resistant material. Many plastics are suitable for this purpose. However, a further requirement is that it be possible to open the housing repeatedly for inspection, maintenance and repair of the equipment carried therein, and that the corrosion-proofing coating retain its integrity after re-assembly of the housing without having to again corrosion-proof the housing, e.g. by recoating the completed housing, which would be extremely inconvenient. Similarly, of course, the plastic coating cannot be permitted to interfere with the explosion-proof nature of the housing.
The prior art shows no suitable way of fabricating a corrosion-proof housing which can be disassembled and reassembled without destruction of the coating. Beene U.S. Pat. No. 3,535,136 shows a method for joining two pieces of threaded conduit which provides a continuous corrosion-proof coating thereon. This involves fabrication of a coating in such a way that a male portion of the corrosion-resisting coating on one piece of the conduit extends into a female portion of the coating on the other conduit member, and is in compression therewith upon assembly. This approach is effective but would be very difficult to fabricate because of the complex shapes required. In particular, this method is not amenable to coating by dipping, which is much the most practical way of coating such things as housings, particularly the irregularly shaped housing which are frequently of use. The difficulty with corrosion-proofing housings by dipping the complete housing is that access must be provided to the interior of the housing. A complete housing can be separated into its components after dipping by simply cutting along a join line, generally in the vicinity of the parting line between the two or more portions of the housing. However, such a cut will inevitably leave a gap through which corrosive gases and the like can enter, thus rendering the assembly non-corrosion-proof; furthermore, the portions will ordinarily not be interchangeable.